Digg never had much in the way gray/illicit content; The AACS key was only posted because it was newsworthy (and can a 128bit number even be considered illicit?)

There were a bunch of other issues at the time centering around digg power users (like MrBabyMan), and a perceived lack of action/communication from the digg staff. The disconnect had been boiling away under the surface for years.

The much bigger issue that the front page of digg at that time was increasingly just links that hit the front page of reddit 12-24 hours earlier. Users increasingly choosing to cut out the middle man and get their content directly from reddit. And at the same time, many fell in love with reddit's much better commenting system.

The censorship was just the catalyst for it all to finally boil to the surface, and the only news-worthy event to happen around that time. It might have been the final straw for some people, but for most it was tangentially related, at best.